Low-speed Machines Research Articles

Personal inhalable paper dust exposure and potential determinants among paper industry workers in Ethiopia.

Excessive paper dust during paper production may harm the workers' respiratory health. We wanted to assess the inhalable paper dust levels and its determinants among paper industry workers. A study was conducted in Ethiopia to assess the level of personal inhalable paper dust exposure among four paper mills. A total of 150 samples were collected using the IOM sampler attached to Side Kick Casella pumps at a flow rate of 2L/min. The samples were analyzed in Nemko Norlab, Norway. Linear mixed-effect models were applied to identify determinants of inhalable paper dust. The geometric mean of personal inhalable paper dust was 3.3mg/m3 with 80% of the measurements exceeding the Swedish occupational exposure limit (OEL) of 2 mg/m3. The linear mixed-effects model showed that the level of dust was 28% higher when using high-speed than when using low-speed rewinding machines, while paper mills with an average of more than four machines per job group had 22% higher exposure than paper mills with a lower number of machines. Furthermore, working in packing and preparation was associated with higher dust exposure than in other areas. The dust exposure levels were above the Swedish OEL for 80% of the samples. This indicates that preventive measures should be established in the industry. The exposure model identified high-speed rewinding machines, a high number of machines, and work in preparation and packing as associated with high levels of paper dust exposure.

Substantiation of the possibility of gas liquefaction in oil–free low–speed refrigeration compressors

BACKGROUND: Existing refrigeration machines contain four main units, i.e., compressor, condenser, expander, and evaporator that perform the refrigeration cycle. Currently, the liquefaction of the refrigerant occurs in the condenser. The creation of the conditions under which condensation of the working fluid would occur in the compressor unit would make the development of a compact refrigeration machine possible by eliminating the condenser from it.
 AIMS: This work aims to investigate the possibility of creating a compact refrigeration machine with the implementation of the condensation process of the working fluid in the compression chamber of the compressor.
 MATERIALS AND METHODS: The object of the study is a low–speed compressor, in which the pressure ratio significantly exceeds known analogs and simultaneously the temperature is significantly lower than that of high–speed machines because of the creation of conditions under which compression occurs with polytropic indicators below 1.08. The research method involves determining the gas temperature at critical pressure and comparing the obtained result with the critical temperature. The system of equations and assumptions used relates to the model with lumped parameters of the working fluid.
 RESULTS: The results obtained on the compression of such refrigerants as ammonia, carbon dioxide, R12, R22, and Freon–134a showed the possibility of obtaining the required pressures in a low–speed machine at temperatures significantly below the critical temperature.
 CONCLUSIONS: This work examines and proposes to study further those working fluids of refrigeration machines that can go into the liquid phase in a low–speed compressor unit because of their characteristics and operating parameters in the refrigeration machine. Further experimental confirmation of this will enable partial or complete elimination of the condenser unit in the refrigeration machine.

Contribution to Improve Magnetic Performance and Torque Ripple Reduction of the Low-Speed DSPM Machine

This article deals with the performance improvement of a toothed pole variable reluctance machine excited by permanent magnets housed in the stator yoke. The objective was to reduce the electromagnetic torque ripples caused by the structure geometry and by the supply technique. The machine was designed to meet the specifications of a small wind energy conversion system. The proposed solution improved the electromagnetic design of the new structure in order to minimize the variation of the reluctance. This improvement was obtained by action on the geometry of the structure (the location of the permanent magnets), by action on the stator and rotor tooth pitch, and by the application of an indirect control strategy called torque sharing function. The PSO optimization algorithm was applied in the first part for the optimization of the machine’s global parameters to maximize torque density and then, in the second part, for the research of the optimum tooth pitch parameters to minimize torque ripple. Static and dynamic performances were obtained using 2D-FEM and MATLAB/Simulink software. The results reveal that by action on the stator/rotor tooth pitch, the ripple torque was reduced by about 53%, and by approximately 76% with the used command technique.

Cascaded Modular Multilevel Converter and Cycloconverter Based Machine Drive System

Low-speed drive is one of the challenges for modular multilevel converters (MMCs) due to large capacitor voltage fluctuation. In this article, a cascaded MMC and cycloconverter (CCV) based machine drive system is proposed to ensure stable operation of medium-voltage and low-speed machine. The MMC provides medium-frequency ac voltage for the CCV, and the CCV converts the medium-frequency ac input to low-frequency ac output required by the machine. Detailed analysis about MMC's operation frequency, device current stress, and submodule (SM) capacitance are given in this article. Proposed drive system can operate at zero/low frequency under rated load torque, while the SM capacitance is much smaller than that in existing methods. Simulation and experimental studies are conducted, and the results verify the effectiveness of the proposed system.

Research on Slot-pole Combination in High-power Direct-drive PM Vernier Generator for Fractional Frequency Transmission System

Offshore wind energy is an important part of clean energy, and the adoption of wind energy to generate electricity will contribute to the implementation of the carbon peaking and carbon neutrality goals. The combination of the fractional frequency transmission system (FFTS) and the direct-drive wind turbine generator will be beneficial to the development of the offshore wind power industry. The use of fractional frequency in FFTS is beneficial to the transmission of electrical energy, but it will also lead to an increase in the volume and weight of the generator, which is unfavorable for wind power generation. Improving the torque density of the generator can effectively reduce the volume of the generators. The vernier permanent magnet machine (VPM) operates on the magnetic flux modulation principle and has the merits of high torque density. In the field of electric machines, the vernier machine based on the principle of magnetic flux modulation has been proved its feasibility to reduce the volume and weight. However, in the field of low-speed direct-drive machines for high-power fractional frequency power generation, there are still few related researches. Therefore, this paper studies the application of magnetic flux modulation in fractional frequency and high-power direct-drive wind turbine generators, mainly analyzes the influence of different pole ratios and different pole pairs on the generator, and draws some conclusions to provide reference for the design of wind turbine generators.

Quantitative Comparisons of Outer-Rotor Permanent Magnet Machines of Different Structures/Phases for In-Wheel Electrical Vehicle Application

As one of the key components, low-speed direct-drive in-wheel machines with high compact volume and high torque density are important for the traction system of electric vehicles (EVs). This paper introduces four different types of outer-rotor permanent magnet motors for EVs, including one five-phase SPM machine, one three-phase IPM machine with V-shaped PMs, one seven-phase axial flux machine (AFM) of sandwich structure and finally one hybrid flux (radial and axial) machine with a third rotor with V-shaped PMs added to the AFM. Firstly, the design criteria and basic operation principle are compared and discussed. Then, the key properties are analyzed using the Finite Element Method (FEM). The electromagnetic properties of the four fractional slot tooth concentrated winding in-wheel motors with similar dimensions are quantitatively compared, including air-gap flux density, electromotive force, field weakening capability, torque density, losses, and fault tolerant capability. The results show that the multi-phase motors have high torque density and high fault tolerance and are suitable for direct drive applications in EVs.

A Novel Concentrated-Winding Vernier Pseudo-Direct-Drive Permanent-Magnet Machine

The demand for low-speed (LS) and high-torque electrical machines is increasing in different applications. Previous research showed that dual-stator magnetically geared machines, such as Vernier pseudo-direct-drive machines (VPDDs), can have a high torque density and a high power factor. However, the size of their end-winding can affect heavily their torque density. Based on a distributed winding VPDD, we propose a concentrated-winding split-teeth VPDD (ST-VPDD), which can reduce the size of end-winding and output higher torque density. In this research, a model of the end-winding volume is given. Through preliminary design and finite element model (FEM) analysis, the torque density optimization has been performed to maximize the torque density. Taking the end-winding into account, there is a 93.8% improvement for the torque density, compared to the VPDD, to reach 78.1 Nm/L. After adding a sleeve for mechanical stability, the ST-VPDD still gives a 68.7% improvement compared to the VPDD.

Comprehensive assessment of the strength of the composite fan blade of the main ventilation of the mine

The work is devoted to the development and calculation of the strength of a new composite fan blade of the main ventilation of the mine, including the static and modal analyzes, as well as the stability analysis. The studies took into account the pre-determined aerodynamic loads on the lateral surface of the blade airfoil. The research was carried out by means of the finite element analysis of the thin-walled airfoil structure using the theory of thick multilayer shells. Estimation of the static strength was performed using the Hashin strength criterion. Analysis of the airfoil shell buckling resistance under the action of bending aerodynamic loads was performed using the methods of the linear stability theory. The modal analysis was performed taking into account the prestressed state from the action of static loads. The analysis of the research results testifies to the sufficient static and dynamic strength of the composite airfoil and the possibility of its implementation in a real rotary machine with the correct design of the fastening between the metal part of the blade root and the composite airfoil. The method of designing and analyzing the strength of the fan blade composite airfoil can be used to create new composite elements of turbomachines: the correct selection of thicknesses of different parts of the airfoil allows obtaining a uniform design with rational use of material; the optimal location of the stiffeners inside the airfoil shell avoids its excessive displacement and stress and the buckling effects, as well as achieving the maximal detuning level from the bending natural frequencies of vibrations; the proposed integrated approach to the strength assessment, which takes into account the effect of aerodynamic loads on the blade airfoil in the static analysis and the prestressed state during the modal analysis can significantly improve the accuracy and correctness of calculations. The approach described in the paper is new for low-speed rotary machines, as at present there are no comprehensive methods for designing composite blades of fans and compressors, and there is no mention of specific examples of their implementation in the projects implemented by manufacturers.

Advanced imaging of dentin microstructure

This study aimed to demonstrate the feasibility of using optical coherence tomography (OCT) for locating the sectioning site of a specimen before characterizing the ultrastructural features of dentin surfaces as well as the inner wall of the dentinal tubules (DT) using a field emission scanning electron microscope (FESEM). Eight sound human molar teeth were extracted, examined via cross-polarization optical coherence tomography (CP-OCT), embedded, and hemisectioned using a low-speed diamond sawing machine. Next, each sectioned surface was further trimmed, polished, and examined under a confocal laser scanning microscope (CLSM) to locate the target area on the superficial dentin. Subsequently, each section was gold-coated and examined using FESEM. Backscattered reflection from the dentin layer was less than that from the enamel under CP-OCT. Distinct reflections from certain enamel and dentin microstructures were observed before sectioning the specimens. Areas with enamel cracks and dentin defects were identified and avoided during sectioning. At the micron level, the CLSM images exhibited a homogenous distribution of the DT orifices. Low magnification FESEM images showed intertubular dentin as a loosely condensed globular layer with shallow grooves in between, whereas peritubular dentin exhibited more organized condensation of apatite crystals surrounding the DT orifices. High magnification of the DT revealed a cross-linking layer of mineralized collagen network extending in the peri-intratubular lumen, with scattered globules of matrix vesicles. CP-OCT enabled the realization of rapid initial scanning and image acquisition with high contrast at the micron scale before profound insights into dentin ultrastructures at the nano scale were provided by FESEM. The variations in structural densities of the dental tissues significantly affected the image contrast and helped identify underlying structures.

Loss Study of Dual Stator Low Speed High Torque Synchronous Motor with Hybrid Rotor

Low speed and high torque machines are widely used in industrial production, oilfield mining, wind power generation, etc. Low speed high torque motors have large internal space, in order to make full use of internal space this paper proposes a dual stator low speed high torque synchronous motor. The rotor adopts a surface-mounted permanent magnet rotor structure on one side, and a spliced reluctance rotor structure on the other side. A magnetic ring is added in the middle to make permanent magnet and magnetic resistance independent of each other. The motor has a special structure, and the loss distribution is different from that of a normal motor. The loss will affect the performance of the motor. This paper establishes the iron loss model considering the effects of alternating magnetic field, rotating magnetic field, and harmonics. Considering the influence of temperature on copper loss. Then establish a mathematical model of core loss and copper loss. Then studying the motor iron loss and copper loss distribution characteristics. Finally, the results are compared with the finite element method (FEM) to verify the effectiveness of the loss calculation in the paper.

Root Crack Identification of Sun Gear in Planetary Gear System Combining Fault Dynamics with VMD Algorithm

Planetary gearbox is widely used in various low-speed machines due to its large transmission ratio. However, the gears in a planetary gearbox are prone to the mechanical faults due to the complex dynamic heavy load. Vibration frequencies caused by an early tooth root crack of sun gear are usually difficult to accurately extract, so its fault diagnosis is one of the main challenges of planetary gearbox reliability. In this paper, a simplified tooth root crack model of sun gear is proposed, and then a rigid-flexible coupled dynamics model of the whole planetary gear system is constructed. By the numerical simulation, the fault frequencies caused by a tooth root crack of sun gear are obtained. A Variational Mode Decomposition (VMD) algorithm for the vibration frequency extraction is proposed. The measured vibration signals are decomposed into the sparse Intrinsic Mode Functions (IMFs) by the VMD, and then the IMFs are further analyzed by the spectral method to accurately extract the crack-induced frequency components. The experimental results show that the proposed dynamics model and VMD method are feasible; an error between the characteristic frequencies from the tested signal analysis and the theoretical calculation is less than 1%.

Impact of the Intermittency Movement of Center Pivots on Irrigation Uniformity

A computer model was developed to simulate the varying depths of water applied to the ground due to the intermittent movements of a typical center pivot. The stop–go model inputs include the sprinkler application depth, the sprinkler pattern, that pattern’s wetted radius, the center pivot’s % timer setting, the move cycle time, and the end tower maximum travel speed. The model outputs were the depth of application in the pivot’s movement direction, the distribution uniformity (DU), and the coefficient of uniformity (CU). The results revealed that the pivot circular application uniformity is mostly a function of the move distance as a percent of the sprinklers’ wetted radius. This, in turn, is a function of the percent timer setting, the cycle time, and the end tower travel speed. Due to this, the high-speed center pivots had corresponding lower application uniformities compared to low-speed machines, and sprinklers with larger wetted radii resulted in better uniformity. Shortening the cycle time also resulted in higher uniformity coefficients. Based on these results, it is recommended that the run time be set based on the pivot end-tower’s travel speed and sprinkler wetted radius, such that the end tower move distance is equivalent to the sprinkler wetted radius. This will reduce wear to the tower motors due to the on–off cycling, especially for slow travel settings and for sprinklers with larger wetted radii. The ponding depths at different percent of the move distance, for the potential runoff, were estimated, which were set to be equivalent to the wetted radius.

Selected faults of low-speed machines, analysis of diagnostic signals

In an industrial environment, a large part of the solutions used in machine parks is based on rotating systems. Therefore, the branches of diagnostics in this area are subjected to extensive research so that they effect with more and more new solutions. This article presents the problem of selected most common faults in a low-speed machinery environment. Presented chapters define the concept of symptoms and diagnostics and define its goals. Selected issues of the analysis of diagnostic signals were also discussed.

Modeling of airgap flux density for the study of stator core vibration in low speed synchronous machines

Purpose This paper aims to develop models and simulations focused on the prediction of electromagnetic forces acting on the stator core of a synchronous machine. It contributes to the study of stator core vibrations. Design/methodology/approach An analytical model based on the rotating fields’ theory including the damper winding contribution was developed. Such model allows the comprehension of airgap magnetic field distribution and the consequent pressure distribution. Focus was given to the pressure sub-harmonics due to the usual fractional winding configuration of low speed machines. A comparative numerical model was also developed and applied to an example laboratory machine. Partial validation measurements were performed. Findings The paper provides the predicted electromagnetic forces and the relative influences of damper winding and teeth tangential forces on each pressure harmonic. It is shown by how much such effects can influence the amplitude of pressure sub-harmonics from a fractional stator winding. Research limitations/implications The performed validation measurements were based on the airgap field distribution, but the resulting core vibration at load was not measured. Therefore, researchers are encouraged to perform additional tests for improved validation. Practical implications The obtained models and results are of great importance for the design phase of new generators and for the diagnosis process of existing machines with core vibration problems. Originality/value As a contribution of this paper, the magnitude of indirect effect of tangential forces and the effect of damper winding are comparatively quantified for each pressure harmonic. The given approach contributes to the relative evaluation of these effects especially on the sub-harmonics from the fractional stator winding.

Applying Foil Queue Microelectrode with Tapered Structure in Micro-EDM to Eliminate the Step Effect on the 3D Microstructure's Surface.

When using foil queue microelectrodes (FQ-microelectrodes) for micro electrical discharge machining (micro-EDM), the processed results of each foil microelectrode (F-microelectrode) can be stacked to construct three-dimensional (3D) microstructures. However, the surface of the 3D microstructure obtained from this process will have a step effect, which has an adverse effect on the surface quality and shape accuracy of the 3D microstructures. To focus on this problem, this paper proposes to use FQ-microelectrodes with tapered structures for micro-EDM, thereby eliminating the step effect on the 3D microstructure’s surface. By using a low-speed wire EDM machine, a copper foil with thickness of 300 μm was processed to obtain a FQ-microelectrode in which each of the F-microelectrodes has a tapered structure along its thickness direction. These tapered structures could effectively improve the construction precision of the 3D microstructure and effectively eliminate the step effect. In this paper, the effects of the taper angle and the number of microelectrodes on the step effect were investigated. The experimental results show that the step effect on the 3D microstructure’s surface became less evident with the taper angle and the number of F-microelectrodes increased. Finally, under the processing voltage of 120 V, pulse width of 1 μs and pulse interval of 10 μs, a FQ-microelectrode (including 40 F-microelectrodes) with 10° taper angle was used for micro-EDM. The obtained 3D microstructure has good surface quality and the step effect was essentially eliminated.

The magnetic circuit analysis of the transverse magnetic flux generator in no-load mode

Purpose. The transversal flux generators are very perspective machine type. They can use low wind or water flow to transform their energy into the electricity with good efficiency value. Obtaining the dependence of the length of the permanent magnet on its magnetizing force on both radii of the rotor. This ratio allows us to correctly select the dimensions of the standardized permanent magnets to excite the generator. This dependence of permanent magnet length allows us to better analyze the electromagnetic processes in transverse magnetic field generator. Methodology. Analytic and computer calculation of magnetic field of the transversal magnetic flux generator in no-load mode. The analytical methodology must be proved by finiteelement method using the 3D simulation in the modern and powerful software such as Ansys Maxwell. It allows us to compare methodology of TFM design and find the most optimal method for TFM design in accordance with fast and accuracy design process. Results. An equivalent circuit is presented for the magnetic system of the transverse magnetic flux generator, which is characterized by a disk design of the rotor and excitation from permanent magnets in no-load mode. On the example of TFM-32-180, the principle of its solution using the working diagram of a permanent magnet is presented. Originality. The analytical calculation of the correct selection of the standardized permanent magnets dimensions to excite the transversal magnetic flux generator in no-load mode. Practical value. This generators work as a low speed machine and have a rather simple construction. It can be used as high effective machine in low speed rivers or wind turbines installations. Therefore, quality and accurate design process is a practically evaluated. Getting the possibility to analytically design the transversal magnetic flux generator more accurately is a good practical value of this perspective type of the machine.

Abrasive water jet machining of fly ash and metakaolin based geo-polymers

In the present study, the abrasive water jet machining (AWJM) of geopolymers prepared from fly ash, metakaolin and sand is discussed. The samples were prepared from sodium promoter, fly ash / metakaolin and sand. The process of activation was made using a 10M sodium hydroxide solution combined with a sodium silicate solution (the ratio of liquid glass - 1:2.5). To produce geopolymers, flakes of technical sodium hydroxide were used and an aqueous solution of sodium silicate (R-145) with a molar module of 2.5 and a density of around 1.45 g/cm3 the tap water. The alkaline solution was prepared by means of pouring the aqueous solution of sodium silicate over the solid sodium hydroxide. The solution was mixed and left until its temperature stablised and the concentrations equalised, which took around 2 hours. The fly ash, sand and alkaline solution were mixed for around 10 minutes using a low-speed mixing machine (in order to obtain a homogeneous paste). The paste was allowed to dry in the shade. The paper investigates the AWJM studies on the prepared geopolymer specimens with varyied input parameters such as standoff distance (1.2 and 3 mm), water pressure (120, 140 and 160 MPa) and feed rate (5, 10 and 15 mm/min). The output parameters such as kerf angle and material removal rate (MRR) were studied with the varying combination of input parameters. From the results, the optimal parameters for machining the geopolymer composites were interpreted.

Design and analysis of a new axial flux permanent magnet synchronous generator for wind

The paper deals with a new design of a low-speed disk permanent magnet axial flux synchronous machine for decentralized power generation, which has improved weight-size parameters. In the new design the value of the air gap value is reduced by removing all inter-coil connections from the gap and also a concentrated winding with a high winding coefficient is applied. A two-rotor prototype of this design is created (150 W, 83 V, 250 rpm) and its magnetic circuit and the concentrated windings arrangement are described, as well as the results of the machine experimental study. The 2D finite element analysis is used to determine the effect of the air gap value effect on the disk slotless generator parameters. The method of rational choice of the machine main dimensions and the parameters of its winding according to nominal data and electromagnetic loads limitations are presented. Comparison of parameters and characteristics of a 20-pole-pair 5 kW synchronous wind generator with the new design and cylindrical one with tangential magnetization is performed. The proposed slotless design exceeds the cylindrical one in efficiency and requires less material costs. The limitations are the higher value of the outer machine diameter and the required large magnets mass.

A Design Study on 40 MW Synchronous Motor With No-Insulation HTS Field Winding

This paper presents a design study on a 40 MW synchronous motor having no-insulation (NI) high-temperature superconductor (HTS) field coils. An in-house analytic code was used to obtain a first-cut design based on the published parameters of the AMSC 36.5 MW ship propulsion motor as a reference. Then, design refinement was followed using the finite-element method to more accurately simulate electromechanical behaviors of the motor. After the final design was completed, transient torque responses of the NI motor, in no load and full load conditions, were simulated with our new equivalent circuit model to consider the nonlinear behaviors of the NI field coils, and compared the results with those of its insulated counterpart. The overall torque response of the NI machine was essentially identical to that of the insulated one, though a notable discrepancy was observed at the moment when the rotor acceleration started and ended. The results may imply that the NI field coils play a role as an effective damper in perspective of the torque response. The results demonstrate a potential to use the NI HTS field coils for a low-speed synchronous machine such as the ship propulsion motor.

Lightweight design of direct-drive wind turbine electrical generators: A comparison between steel and composite material structures

Direct-drive generators for wind turbines are high torque, low speed machines which require a heavy robust structure to maintain the air-gap clearance open and stable. The mass of the structural material can be assessed at the early stages of the design process for radial-flux generators. By using low density materials, such as composites, the entire mass of the machine can be significantly reduced. A comparison between steel structures and structures made with composite materials working under the same loading conditions is made using small scale (100 kW) and large scale (3 MW) generator models. Potential improvements to the lightweight proposed structures are also suggested.